The present invention relates to data storage devices that employ aerodynamically supported transducing sliders for reading and recording magnetic data, and more particularly to structure and circuitry for controlling the flying heights of magnetic data transducers carried by such sliders.
In typical magnetic data storage devices, magnetic disks with flat recording surfaces are mounted rotatably and magnetic data transducing heads are positioned in close proximity to the recording surfaces, each head movable generally radially with respect to its associated disk. In higher capacity devices, the disks are rotated at high speeds to create an air cushion or bearing that supports each transducing head at a controlled distance from its associated recording surface. The transducing heads contact their associated disks only when the disks are either stationery, accelerating from a stop, or decelerating to a complete stop.
Designers of magnetic disks continually strive to increase the density at which the magnetic data can be stored. One factor that limits storage densities is the transducing head flying height. As discrete data storage areas are placed more closely to one another, the transducer must be positioned more closely to the recording surface to distinguish between adjacent storage areas. In recent year, transducing head flying heights have been decreased from levels greater than about 10 microinches, to levels of less than about 4 microinches, largely due to improved techniques for reducing media surface roughness. Further reductions in flying height are enabled by a super smooth polishing of media surfaces in data recording areas while also providing an adjacent head contact zone, textured to avoid stiction problems. An example of this approach is shown in U.S. Pat. No. 5,062,021, (Ranjan et al) assigned to the assignee of this application.
There are several factors that limit the reduction in slider flying height. These fcctors might reasonably be ignored at flying heights of about 10 microinches, but would become major concerns at flying heights on the order of 1-2 microinches. These include variations in the sliders themselves, variations in the structure that supports the sliders, and media surface roughness.
More particularly, normal tolerances in slider fabrication lead to structural variations among the sliders in any given batch. Consequently, thie flying heights of sliders in the batch are distributed over a range, although the flying height of each slider individually is substantially constant.
Variations in supporting structure occur primarily in the transducer support arm, the suspension or gimballing structure, slider geometry and load arm. These variations influence the flying height, and the nature of a given slider's reaction to any disturbances, e.g. due to shock or vibration.
Disk roughness also becomes more of a problem at lower slider flying heights. With maximum peaks more likely to protrude into a normal range of slider operation, the probability of unintended and damaging slider/disk contact increases. The risk of damage from these discontinuities is greater at lower slider flying heights.
Thermal effects also are exaggerated by minute slider flying heights. Thermal effects include the natural tendency of materials to expand when heated, quantified by a temperature coefficient of thermal expansion more conveniently called a thermal expansion coefficient. Materials with higher coefficients expand more in response to a given temperature increase. When materials having different thermal expansion coefficients are contiguous and integral, their differing expansion when heated leads to elastic deformations and elastic restoring forces in both of the materials. Reduced flying heights increase the need to take thermal expansion and thermally induced elastic deformation into account.
One proposed design of a slider would drag on the disk surface, thereby more precisely fixing a head/disk spacing based on a peak roughness of the disk surface. Any improvement in setting the transducer/recording surface gap, however, would be at the cost of excessive wear to the slider, media recording surface, or both.
Several patents discuss the use of piezoelectric material in a slider, to adjust the position of a transducer mounted to the slider. For example, U.S. Pat. No. 5,021,906 (Chang et al) discloses a programmable air bearing slider with a deformable piezoelectric region between leading edge and trailing edge regions. The deformable region is controlled electrically to change the angle between the leading and trailing regions, thus to change the position of a transducer mounted to the trailing region.
U.S. Pat. No. 4,853,810 (Pohl et al) concerns a magnetic transducing head including a body and a piezoelectric layer adjacent the body. The piezoelectric layer is operable to control the head/disk gap, based on sensing a tunnel current across the gap between the recording surface and a tunnel electrode on the slider.
In U.S. Pat. No. 4,605,977 (Matthews), a cantilevered beam mounted to a slider supports a magnetic transducer at its free end. The beam includes a flexible vein and piezoelectric transducers on opposite sides of the vein, used in combination with a piezoelectric driver to adjust the position of the magnetic transducer.
The piezoelectric sliders are difficult to fabricate. Large activation voltages are required for piezoelectrically deforming materials a sufficient aLmount to control the transducer position. Piezoelectric deformation schemes can take thermal expansions and elastic deformations into account indirectly, but cannot be employed to limit or otherwise influence these phenomena.
Therefore, it is an object of the present invention to provide a magnetic transducing slider incorporating non-piezoelectric means to control the flying height of a magnetic transducer carried by the slider, independently of the flying height of the slider.
Another object of the invention is to mount a magnetic transducer to an air bearing slider body in a manner that enables controllably adjusting the transducer position relative to the slider body by controlling an operating temperature of the slider.
A further object is to provide a magnetic data transducing apparatus in which positionable adjustments of a magnetic transducer, relative to a slider body carrying the transducer, are controlled at least in part responsive to sensing slider temperature.
Yet another object is to provide a process for selecting a spacing between a magnetic transducer and an air bearing surface of the slider carrying the transducer, to achieve substantial uniformity in transducer flying heights among multiple sliders, despite a variance in the corresponding slider flying heights.